Allergy Introduction, Types, Mechanism of Allergy, Testing for Allergy

1. ALLERGY

2. INTRODUCTION TO ALLERGY AND ITS TYPES
 Allergy is defined as “the abnormal or unusual response to a substance by human
body is called allergy” OR
 “The harmful reaction to the external substance is known as allergy”
 The external reaction is known as allergens.
 Allergies occur when your immune system reacts to a foreign substance — such as
pollen, bee venom or pet dander — or a food that doesn't cause a reaction in most
people.

3. • Your immune system produces substances known as antibodies. When you have allergies, your immune
system makes antibodies that identify a particular allergen as harmful, even though it isn't. When you come
into contact with the allergen, your immune system's reaction can inflame your skin, sinuses, airways or
digestive system.
• The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis —
a potentially life-threatening emergency. While most allergies can't be cured, treatments can help relieve
your allergy symptoms.

4. ALLERGENS
Allergens: Allergens are inciting agents of allergy i.e. The substances capable of sensitizing the body in such
a way that an unusual response occurs , in hypersensitive person.
Allergenic extracts: Theses are the substances used for diagnosis and treatment of allergic diseases and are
concentrated solutions or suspensions of allergen.
• These are antigenic substances capable of sensitizing the body in such a way that unusual responses occur
in the hypersensitivity individuals. Almost any substances weather of biological, chemical or synthetic
origin, may prove to be allergens.
• The substance such as pollens, dander's, dust etc. as natural allergens.
• Allergens are protein or glycoprotein .

6. ALLERGY CAUSING FACTORS
• An allergy starts when your immune system mistakes a normally harmless substance for a
dangerous invader. The immune system then produces antibodies that remain on the alert for
that particular allergen. When you're exposed to the allergen again, these antibodies can
release a number of immune system chemicals, such as histamine, that cause allergy
symptoms.
Common allergy triggers include:
 Airborne allergens such as pollen, animal dander, dust mites and mold
Certain foods particularly peanuts, tree nuts, wheat, soy, fish, shellfish, eggs and milk

7. ALLERGY CAUSING FACTORS
 Insects stings, such as from a bee or wasp
 Medications, particularly penicillin or penicillin-based antibiotics
Latex or other substances you touch, which can cause allergic skin reactions

8. CLASSIFICATION OF ALLERGY ON THE BASIS OF THEIR LOCATION
Allergic reactions may be of two types:
A. Localized reactions: If the state of shock is confined to the area of the introduction of the
allergen, the condition is a localized reaction. e.g. when pollen grains are inhaled which
cause sinusitis due to allergic reactions. The sinusitis is restricted to the face so allergic
reactions are localized.
B. Generalized reactions: If it is extended beyond this area it may be generalized or
constitutional reactions. The constitutional reactions are produce in the some patients by
the injection of penicillin preparations and extremely uncomfortable and sometime
dangerous and even fatal.

9. CLASSIFICATION OF ALLERGY ON THE BASIS OF THEIR NATURE
There are different types of Allergens:
INHALANT ALLERGENS
INGESTANT ALLERGENS
INJECTANT ALLERGENS
CONTACTANT ALLERGENS
INFECTANT ALLERGENS

10. I. INHALANT ALLERGENS
• Inhalant allergens are air borne substances as chemicals, causing respiratory disease,
inflammation in nose and lungs.
• Inhalant allergies caused by environmental factors such as pollen, pets, house dust, mites and
moulds.

11. Symptoms:
 Sneezing
Lacrimation
Coughing and post nasal drip
Itching eyes, nose and throat.
Allergic shiner
Allergic salute
Watering eyes, conjunctivitis.
The condition is known as ‘sinusitis’ or ‘hayfever’.

12. II. INGESTANT ALLERGENS
• Allergens which are present in food stuff and swallowed are termed ingestant (food
allergy).
• A food allergy is an immune system response to a food.
• When foods are digested and the nutrients are absorbed, substances in the food
(ingestant allergens) stimulate allergic response. These reactions cause a number of
allergic symptoms.
• Some most common food allergens ingested by patients are milk, egg, peanut, fish,
shellfish, soy, wheat, orange juice, cod liver

13. Symptoms:
Food allergens ordinarily cause GIT
symptoms, but they may also cause
Skin rash
Puffed lips and tongue
Migraine
Rhinitis
Bronchial asthma
Severe cases of eczema of hands.

14. III- INJECTANT ALLERGENS
• The injectants (injectable preparations and insects) cause
allergy in hypersensitive person, this allergic conditions is
known as injectants allergy.
• Injectants are the substances injected into the skin,
muscles, joints or blood vessels. Serum, antitoxins,
vaccines immunizations, & drugs are among injected
substances.
• The natural sources of injectable allergens are produced by
the sting of bees, hornets and wasps.
• In addition to penicillin products, other injectable that may
cause allergies are liver extract, antitoxins and the
glandular products.

15. Symptoms:
Itching of the palms of hands and soles of feet
Erythema
Peeling of skin

16. IV-CONTACTANT ALLERGEN
• “Any group of allergens that elicit manifestations of induced sensitivity by direct contact
with the skin or mucosa is known as contact allergen”
• Aeroallergens, such as the various pollen grains containing oils, trichomes from various
leaves, flowers and small fragments of plants tissue carried by smoke originating from bush
fires, grass fires and burning leaves are also cause for contact allergens.
• A Number of plants products used as additives in cosmetics and perfumes are irritants and
cause skin allergy to some hypersensitive individuals.
• Wool fat in cosmetics, soap and soap powders, plain detergents and enzyme detergents, nail
polishes, hair dye and hair spray are also included among the major cause of contact
dermatitis.

17. • Direct contact with the skin of the animal can result in
allergic symptoms from contactants. Cosmetic, soaps,
oils, detergents, latex products, formaldehyde & various
plan oils such as those from poison ivy, oak can be
contactant allergies.

18. V- INFECTANT ALLERGEN
• “Allergy caused by the metabolic product of living micro-organism in the human
body”.
• The continual presence of certain types of bacteria, protozoa's, molds, helminthes
and other parasites in the body of human being are responsible for chronic
infection.
• In such patient bacterial metabolic waste are considered to be infectant allergens.

19. • The chronic bacterial infection of the bronchioles,
known as bronchiectasis, in which the constant
presence of bacterial wastes may sensitize the
allergic individual, is an example. Thus, the person
may exhibit allergic symptoms but does not
respond positively to skin tests for inhalant
allergens. In this case, the bacterial metabolic
wastes are considered infectant allergens.
• In a manner somewhat similar to the infectants,
parasitic organisms may sensitize the human body.
• Invasions of hookworms, tapeworms, pinworms,
threadworms, dermatophytes and other forms have
caused allergic response in susceptible individuals.

20. MECHANISM OF ALLERGY
Basic:
• The mechanism involves immunoglobulin E antibodies (IgE), part of the
body's immune system, binding to an allergen and then to a receptor on
mast cells or basophils where it triggers the release of inflammatory
chemicals such as histamine.
• An antibody is a protein produced by our immune system, which circulate
in the bloodstream and help to remove any substances or organisms, such
as bacteria or viruses, which has invaded our body.

21. IMMUNOGLOBULIN E (IgE ANTIBODY)
• It constitutes less than 1% of the total serum.
• It is mostly found in lining of respiratory and intestinal tracts.
• It has a molecular weight of 190,000 Da with a half-life of 2-3 days.
• IgE is a heat labile protein because it is easily inactivated at 56°C in 1
hour.
• Two heavy polypeptide chains along with two light chains joined together
with disulfide bonds comprising the whole IgE molecule.

22. • The IgE antibody is one of five different classes of antibody made by our immune system.
The other four are: IgM, IgG, IgD, and IgA. IgE antibodies originally evolved to give the
body a way of protecting itself from parasites. However, it is also specifically targeted at
allergens.

23. ENTRANCE OF ALLERGEN
• When an allergen enters our body, a person with an inherited
predisposition to this allergen will begin to develop a specific type of
antibody called immunoglobulin E (IgE).
Binding to an allergen:
• IgE binds, through its Fc portion, to high affinity receptors expressed on
mast cells, leaving its allergen specific receptor site available for future
interaction with allergen.

25. ROLE OF B-LYMPHOCYTES
• All immunoglobulins including IgE are made by B-lymphocytes, a
specific type of white blood cell. The B-lymphocyte’s antibody production
is regulated by Helper T-lymphocytes, another type of white blood cell. In
addition, macrophages, cells that ingest pieces of foreign substances,
assist T-lymphocytes to prompt B-lymphocytes to make more IgE.

26. MAST CELL
Where they found:
• Mast cells are located at the boundaries between tissues and the external
environment. For example, at mucosal surfaces of the gut and lungs, in the skin and
around blood vessels.
• They serve as a first line of defense against antigens entering the body due to their
location in the skin and mucosa.
Activation:
• In allergic reactions, this release occurs when the allergy antibody IgE, which is
present on the mast cell surfaces, binds to proteins that cause allergies, called
allergens. This triggering is called activation and the release of it’s mediators is
called degranulation.

28. INFLAMMATORY MEDIATORS
• Mast cells play a central role in inflammatory
and immediate allergic reactions. They are
able to release potent inflammatory mediators,
such as histamine, proteases, chemotactic
factors, cytokines and metabolites of
arachidonic acid that act on the vasculature,
smooth muscle, connective tissue, mucous
glands and inflammatory cells.

29. DEGRANULATION
• As degranulation occurs, it causes the mast cell or basophil to release a
series of chemicals that orchestrate the allergic reaction. Within every
mast cell or basophil are 500 to 1500 granules containing more than
thirty different allergy-causing chemicals. The best known chemical that
is released is histamine. Histamine causes itching if released in the skin,
wheezing if released in the lung, and contributes to a loss of blood
pressure if released throughout the body.

30. HISTAMINE RELEASE
• Histamine is not only released when the body encounters a toxic substance, it is also
released when mast cells detect injury. It causes nearby blood vessels to dilate
allowing more blood to reach the site of the injury or infection.
Effects of histamine:
• Once released from its granules, histamine produces many varied effects within the
body, including the contraction of smooth muscle tissues of the lungs, uterus, and
stomach, the dilation of blood vessels which increases permeability and lowers blood
pressure and the stimulation of gastric acid secretion in the stomach.

31. ALLERGIC INFLAMMATION
• Allergic inflammation is often classified into three temporal phases.
i. Early-phase reactions are induced within seconds to minutes of allergen
challenge
ii. Late-phase reactions occur within several hours
iii. By contrast, chronic allergic inflammation is a persistent inflammation that
occurs at sites of repeated allergen exposure

33. I-EARLY PHASE REACTION
• The early phase of the allergic reaction occurs within minutes or even seconds following
allergen exposure and commonly referred to as the immediate allergic reaction or Type I
allergic reaction.
• The reaction is caused by the release of histamine and mast cell granule proteins such as
leukotrienes, prostaglandins and cytokines by a process called degranulation.
• These mediators affect nerve cells causing itching, smooth muscle cells causing contraction
(leading to the airway narrowing seen in allergic asthma), goblet cells causing mucus
production and endothelial cells causing vasodilatation and edema.
• Most people experience its symptoms such as sneezing, wheezing, itchy eyes, runny nose,
cough, and hives within one hour after being exposed to an allergen.

34. II- LATE PHASE REACTION
• After the chemical mediators of the acute response subside, late-phase responses can
often occur.
• The late phase which develops 8–12 hours and is mediated by mast cells.
• In the late phase reaction, there is tissues redness and swelling due to the arrival of other
cells to the area, including the eosinophils, neutrophils, and lymphocytes. Cytokines
that are released by the mast cells and basophils act as tiny messengers to call these
other cells to the area of inflammation.
• In the lung, the immediate response begins within minutes or even seconds after
exposure to an allergen. This includes shortness of breath, wheezing, and coughing.
This disappears after an hour or so. Three to four hours later, the late phase reaction
begins. It is also characterized by shortness of breath and coughing, and can last up to
24 hours.

35. III- CHRONIC ALLERGIC INFLAMMATION
• Persistent inflammation induced by prolonged or repetitive exposure
to specific allergens, typically characterized not only by the presence
of large numbers of innate and adaptive immune cells (in the form of
leukocytes) at the affected site but also by substantial changes in the
extracellular matrix and alterations in the number, phenotype and
function of structural cells in the affected tissues.

36. Mild to severe symptoms of Allergy:
• Itching of eyes or face.
• swelling of the mouth, throat, and tongue that
can make breathing and swallowing difficult.
• Hives.
• Abdominal pain.
• Cramps.
• Vomiting.
• Diarrhea.
• Mental confusion or dizziness

37. TREATING ALLERGIC REACTIONS
1. Antihistamines:
• Antihistamines help to treat most minor allergic reactions. These drugs reduce the body’s
production of histamine which reduces all symptoms including sneezing, watering eyes, and skin
reactions.
• Antihistamines come in several forms such as oral pills, dissolvable tablets, nasal sprays, liquids
and eye drops.
• Examples of oral antihistamines include:
• loratadine (Claritin)
• cetirizine (Zyrtec)
• fexofenadine (Allegra)
• levocetirizine (Xyzal)

38. • These include glucocorticoids, epinephrine (adrenaline), mast cell stabilizers, and
anti-leukotriene agents are common treatments of allergic diseases. Others are as
follows;
• moisturizing creams (emollients) to keep the skin moist and protect it from allergens
• calamine lotion to reduce itchiness
• steroids to reduce inflammation
• Nasal decongestants
• Anti-inflammatory medication
• Avoid the allergen
• Use a saline sinus rinse
• Treating environmental factors

39. RISK FACTORS AND CAUSES OFALLERGY
Non-modifiable risk factors:
• Age, family history and genetics.
Modifiable risk factors:
• Exposure to allergens, pollution, passive smoking and environmental factors.
Major causes of allergy include;
• Foods
• Latex
• Medications
• Insect stings
• Toxins interacting with proteins
• Genetics
• Hygiene hypothesis
• Stress
• Other environmental factors

40. TYPES OF ALLERGY TEST
Following are the types of Allergy test:
Allergy skin
testing
Lung
Function test
Blood Test
Food
challenge
test
Drug
challenge
test

41. 1- ALLERGY SKIN TESTING
• Skin allergy testing is a method for medical diagnosis of allergies that attempts to provoke a small,
controlled, allergic response. Allergy skin tests are used to find out which substances cause a person to
have an allergic reaction
Types:
• Skin prick test/skin scratch test: It is the most common type of skin test. This test is done by placing a
drop of allergen extract on the skin on the back and passing a needle through the puncture within about 15
minutes. This test measures specific IgE attached to cells in the skin important in allergies called "mast"
cells. Skin prick testing is usually the first test recommended when an allergy is suspected.

42. • Intradermal test: Intradermal allergy testing is another method of skin
testing to help determine whether an individual is allergic to a specific
allergen. The test involves injection of a small amount of the suspected
allergen under the surface of the skin. After about 20 minutes the area
is examined for a reaction at the site. A typical reaction looks like a
small hive with swelling and redness.
• The intradermal test is more sensitive than the skin prick test and can
usually provide more consistent results
• The intradermal test uses a syringe to inject the allergen extract into the
top layer of skin in the arm, which rises a small bubble on the skin
surface. Like the prick method, a hive will appear indicating an allergic
reaction. First, your health care provider examines the skin either on
your forearm or back and cleans it with alcohol. Then a small amount
of the allergen is injected just under the skin. Lastly, you must wait
about 15 minutes to see how your skin reacts.

43. • Patch test: It can be used to look for the substances that
might be causing contact dermatitis. A suspected allergen is
placed on the skin and covered with a bandage for
48hours.If the patient is allergic, the skin will be red and
peel.
• Allergen is applied to a patch that is then placed on the skin.
• If there are IgE’s (allergic antibodies) in your body, your
skin will become irritated and may itch. This reaction
means you are allergic to that substance.

44. 2. LUNG FUNCTION TEST
• Spirometery:

45. 3. BLOOD TESTS
• Blood tests like RAST and ELISA can test for a range of allergies like food allergies, drug
allergies, seasonal allergies and pet allergies.

46. 4. FOOD CHALLENGE TEST
• During the food challenge test, your child will be given certain foods in increasing amounts.
• After your child swallows each portion, the doctor will wait to see if he or she shows signs of
an allergic reaction.
• If no reaction takes place, your child may be asked to eat a slightly larger portion of that food
type.
• The food challenge test is done at a doctor’s office or hospital. Because of the risk of a severe
allergic reaction, you should never attempt a food challenge at home, unless advised
otherwise by a doctor

47. 5. DRUG CHALLENGE TEST
• A drug challenge is a test where the allergist gives you a small amount of
a drug in gradual doses while observing you to watch for a reaction. If
you have a true allergy or a suspected allergy to a drug, stop taking
the drug.